The present disclosure relates generally to information handling systems, and more particularly to selecting Spanning Tree Protocol (STP) links for communication between information handling systems.
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Information handling systems such as, for example, switch devices, sometime utilize the Spanning Tree Protocol (STP) for transmitting traffic through a network. As would be understood by one of skill in the art, the STP is a network protocol that builds a loop-free logical topology for Ethernet/Layer 2 (L2) networks, and operates to prevent bridge loops and the broadcast radiation that results from them, while allowing a network design that includes backup links that provide fault tolerance if an active link fails. The STP may be utilized to create a spanning tree within a network of connected layer-2 bridges (e.g., the switch devices discussed above), and disables those links that are not part of the spanning tree, leaving a single active link between any two network nodes. The active link provided between any two switch devices may be provided by a “designated port” on a “root/designated switch device” and a “root port” on a “non-root/non-designated switch device” (also referred to a “root-designated pair”), while the non-active links may be provided by a “designated port” on that root/designated switch device and an “alternate port” on that non-root/non-designated switch device (also referred to a “alternate-designated pair”). In many examples, one of the switch devices is selected as a root/designated switch device based on its root bridge identifier being lower than any of the other switch devices, and the active link for each non-root/non-designated switch device may be selected amongst a plurality of different links available between the directly connected root switch device or designated switch device and that non-root/non-designated switch device first based on relative root path costs, then based on the lowest designated bridge identifiers if the root path costs associated with the links are the same, and then based on the lowest designated port identifiers if the designated bridge identifiers associated with the links are the same. The use of the designated bridge identifiers in selecting the active link can raise a number of issues.
Typically, the use of the designated bridge identifiers in selecting the active link provides for the selection of the link provided by a port on the non-designated switch device that received the lowest designated bridge identifier from its directly connected designated switch device as the active link, and the designation of the remaining links provided by remaining ports on the non-designated switch device as non-active links (i.e., links that are blocked from forwarding data traffic.) However, subsequent to this STP active link selection, if a new link provided by a port on the non-designated switch device that is connected to a designated switch device having a lower designated bridge identifier becomes available, the active link selection process is repeated so that the new link may be selected as the active link (i.e., due to it being provided by the port on the non-designated switch device that received the lowest designated bridge identifier from its connected designated switch device.) As such, each time a new port on the non-designated switch device provides a new link to a directly connected designated switch device that becomes available and receives a designated bridge identifier that is lower than that received via the currently active link, the STP triggers a topology-change event and traffic is forced to reconverge on that new link due to its selection as the new active link.
The repeating of the STP active link selection process/reconvergence operations is associated with considerable overhead, including the performance of STP port re-selection operations, hardware port state re-programming, Media Access Control (MAC) address flushing, MAC address re-learning, and/or other STP tasks known in the art. Furthermore, the STP active link selection process/reconvergence operations can also result in traffic disruptions that can lead to data loss. Some conventional STP systems allow a network administrator or other user to fix the root switch device (e.g., via “Root Guard” enhancements available from CISCO® Systems, Inc. of San Jose, Calif., United States), but these mechanisms focus simply on “pinning” the root switch device, and do not provide any way to avoid the recomputations performed via the STP algorithms discussed above when several equal cost paths to a directly connected switch device are provided on available links and result in the reconvergence and traffic disruptions discussed above.
Accordingly, it would be desirable to provide an improved STP link selection system.